Custom Field Search not working correctly

Hi

I am trying to alter the search function of wordpress without using a plugin.

I need the search to search only the post title and the postmeta table where the meta_key = ‘agent_skype’

The query which I am trying to code into the search function is

SELECT DISTINCT * 
FROM  wp_posts 
LEFT JOIN  wp_postmeta ON  wp_posts.ID =  wp_postmeta.post_id 
AND  wp_postmeta.meta_key =  'agent_skype'
WHERE (
 wp_posts.post_title LIKE  '%SearchString%'
)
OR (
 wp_postmeta.meta_value LIKE  '%SearchString%'
)

I have used the following code to search only the post title

function wpse_11826_search_by_title( $search, $wp_query ) {
    if ( ! empty( $search ) && ! empty( $wp_query->query_vars['search_terms'] ) ) {
        global $wpdb;        
		$q = $wp_query->query_vars;        
		$n = ! empty( $q['exact'] ) ? '' : '%';        
		$search = array();        
		foreach ( ( array ) $q['search_terms'] as $term ) 
		$search[] = $wpdb->prepare( "$wpdb->posts.post_title LIKE %s", $n . $wpdb->esc_like( $term ) . $n );        
		if ( ! is_user_logged_in() )            
			$search[] = "$wpdb->posts.post_password = ''";        
		$search = ' AND ' . implode( ' AND ', $search );    }    
		return $search;}
			
		add_filter( 'posts_search', 'wpse_11826_search_by_title', 10, 2 ); 

Which works then I used the below to try and extend the search function to include the custom field

function cf_search_join( $join ) {
    global $wpdb;

    if ( is_search() ) {    
        $join .=' LEFT JOIN '.$wpdb->postmeta. ' ON '. $wpdb->posts . '.ID = ' . $wpdb->postmeta . '.post_id AND '. $wpdb->postmeta . 'meta_key = Agent_Skype';
    }
    
    return $join;
}
add_filter('posts_join', 'cf_search_join' );

function cf_search_where( $where ) {
    global $wpdb;
   
    if ( is_search() ) {
        $where = preg_replace(
            "/\(\s*".$wpdb->posts.".post_title\s+LIKE\s*(\'[^\']+\')\s*\)/",
            "(".$wpdb->posts.".post_title LIKE $1) OR EXISTS (".$wpdb->postmeta.".meta_value LIKE $1)", $where );

    }

    return $where;
}
add_filter( 'posts_where', 'cf_search_where' );

function cf_search_distinct( $where ) {
    global $wpdb;

    if ( is_search() ) {
        return "DISTINCT";
    }

    return $where;
}
add_filter( 'posts_distinct', 'cf_search_distinct' );

When using this it does not return the same results as running the query. Can anyone offer any insight in what I’m doing wrong?

I would prefer not to use a plugin for this, as this is also a learning exercise for me.

Thanks